In particular in the area of microlithography, apart from the use of components designed to have the highest possible precision, it is among other things desirable to position the components of the imaging device, thus for example the optical elements (lenses, mirrors etc.), the mask with the projection pattern to be imaged and the substrate to be exposed, as accurately as possible in relation to one another, in order to achieve a correspondingly high imaging quality. The desire for high accuracy, which lies in the microscopic area at an order of magnitude of a few nanometers or less, is nonetheless the result of the constant desire to increase the resolution of the optical systems used in the manufacture of microelectronic circuits, in order to push miniaturization of the microelectronic circuits to be manufactured.
With the increased resolution and the reduction in the wavelength of the light used which as a rule accompanies this, the desired accuracy properties in the positioning and orientation of the components used naturally become greater. This naturally has an effect, for the low working wavelengths in the UV range used in microlithography (for example of around 193 nm), but in particular in the so-called extreme UV (EUV) range between 5 nm and 20 nm (typically around 13 nm), on the effort that has to be made to meet the high desired accuracy properties in the positioning and/or orientation of the components involved.
For the positioning and/or orientation of the optical elements used in the imaging, in particular in microlithography, usually two different approaches are followed.
According to a first approach, so-called parallel kinematics can be used for this, typically in the form of so-called hexapods, in which six support elements that can be adjusted independently of one another are able to spatially position and orient the optical element typically in all six degrees of freedom. The support elements as a rule in each case restrict precisely one degree of freedom (that is to say the degree of freedom of translation in the direction of the longitudinal axis of the support element concerned), so that a statically determined support of the optical element is achieved. The kinematically parallel arrangement of the support elements offers the advantage of comparatively simple control since for all support elements the same local referencing system can be used in a simple manner so that an adjustment of one of the support elements does not have an effect on the local referencing system of one the other support elements. Such hexapods are for example known from US 2002/0163741 A1 to Shibazaki, the entire disclosure of which is included herein by reference. With such hexapods it can be possible to achieve virtually any positioning and orientation of the optical element within the space available. However, they have a comparatively complex design. In particular, for each of the six support elements a separate, independently operated actuator unit is involved, which can make it difficult to integrate the actuator system into available installation space.
A second approach involves so-called tripods, in which the optical element is supported by three adjustable support elements on a support structure. Each support element restricts in each case precisely two degrees of freedom, so that here also a statically determined support of the optical element is achieved. Such a tripod is known for example from US 2002/0163741 A1 to Shibazaki and WO 2005/101131 A1 otKugler et al., the entire disclosure of both of which is included herein by reference. Such a tripod uses a smaller number of support elements, which involves less installation space. Within certain limits, any adjustment of the spatial position and/or orientation of the optical element is also basically possible using such tripods. However, for this it may be desirable to provide serial kinematics, but, because of the interdependency of the adjusting movements, the control can become more complicated. Further, the comparatively few support points of the optical element, in particular for large and heavy optical elements, however, may represent an undesirable feature of these tripods, because the effects of deformation of the optical element under its own weight (for example the so-called three-wave deformation) may be further exacerbated.